Sound-pick-up device



LEWIS T'. BOPTNSON,

Patented Feb. 10, 193i NETE@ STATES PATENT OFFlCE COMPANY, CORPORATION OF NEW 'YORK SOUND-PICK-UP DEVICE Application filed February 28, 1930. Serial No. 432,220.

My invention relates to sound pick-up devices and particularly to such pick-up devices which cause a small mirror to vibrate in response to sound waves. my invention to provide an improved device of this character which shall be simple, sensitive, etlicient and economical to manufacture.

My invention will be better understood from the following description taken in connection with the accompanying drawing, and its scope will be pointed out in the appended claims.

Referring to thedrawing, Fig. 1 is a plan view of an embodiment of my invention drawn to an enlarged scale; Fig. 2 is a transverse cross-sectional view thereof; Fig. 3 is a fragmentary detail view drawn to a still larger scale; and Fig. 4 shows a modified form of the detail. The sound actuated member or diaphragm 1 is shown clamped between two rings 2 and 3 by means of a plurality of screws 4. I preferably construct the diaphragm of mica and the rings of steel, the mica being under tension such that its natural period of vibration is above the audible range. One method of so tensioning the mica is to insert the rings and mica diaphragm with the clamping screws loosened in a bath of liquid air and while thus immersed to tighten the screws. Upon being restored to room temperature the mica which has a smaller coeicient of expansion than steel will be given the required tension. Secured to the ring 2 by the screws 5 is the plate 6 having the central odset portion 7 fitting within the interior vof the ring 2. Across the central openin 8 of the plate 6 isxthe torsion strip 9 which 1s secured, as by soldering, to the lower face of plate 6 while under tension. Attached to one side of the torsion strip and approximately at the middle of the ring is the small mirror 10 which by its angular vibration is adapted for the reflection of a light beam on a movin sensitive lilm in the case that a sound record is bein made or is directed into a photo-- electric ce1? in the case of a paratus for transformin sound vibrations mto electric vibrations. gIhe vibratory movement of the diaphragm 1 is commumeated to the torsion strip 9 by means of the small pin 12 which it will It is the object of` be noted engages the torsion strip adjacent one edge thereof so that the vibratory movements of the diaphragm cause angular vibrations of the torsion strip.

For the purpose of preventing the torsion strip from being moved bodily and for limiting the .vibrations of the strip to angular movements I have provided the abutment member 14 which is adjustably mounted on' the ring 6 and which has the two arms 15 extending to the rear of the torsion strip. Each arm 15 is shown having an inset 16 provided with a knife edge 17 which extends longitudinally of the strip and which engages the same midway between its two edges. The abutment member is adjustably mounted upon the slide 19 and by means of the adjusting screw 20 may be raised or lowered so as to be moved into proper engagement with the torsion strip. The slide 19 is attached to the plate 6 by the two screws 2l which pass through slotted openings therein and by means of the thumb screw 22 carried by the block 23 the slide and the abutment member may be adjusted transverselyof the torsion strip. While I have shown and described the abutment member as having the knife edge Vmembers 16 for engaging the torsion strip, I

may in certain cases use small 4, instead of the knife edge members, which pins will make point cont-act with the torsion strip. With this construction it will be seen that the vibratory movements of the diaphragrn are transmitted through the small pin 12 to the torsion strip where ,the movement is converted into angular vibration. By the provision of the abutment member having its pins 24, see Fig.

knife edges engaging the torsion strip inter- I mediate the edges thereof the movement of the torsion strip is limited to angular movement which thereby reaches a maximum value for a given vibratory movement of the diaphragm.

I have chosen the particular/ embodiment described above as illustrative of my invention and it will be apparent that various modifications may be made without departinF from the spirit and scope of my invention w ich modifications I aim to cover by the appended claims.

What I claim as new and desire to secure by Letters Patent of the United States, is,-

1. A sound pick-up device comprisin a Y. torsion member, a mirror supported there y, Y 5 a sound actuated member connected with said 'torsion member to cause a torsional vibration thereof, and means arranged to engage the torsion member for limiting the movement thereof to torsional vibration. 2. A sound pick-up device comprising a torsion member, a mirror supported thereby,

a diaphragm, means connecting the diaphragm with the torsion member at a point adapted to cause torsional vibration thereof and means associated with the torsional memv berfor preventing displacement bodily thereof without restricting the torsional vibration thereof. A

3. A sound pick-up device comprisingI a zo torsion strip, a mirror secured thereto, a diaphragm, lmeans connecting ythe diaphravm with the strip at a point adjacent one edge of the strip, and an abutment member ar- `ranged'to engage the strip at a point intermediate its e ges. 4. A sound pick-up device comprisin a torsion strip, a mirror secured thereto, a 'aphragm, means connecting the diaphra with the strip at a oint adjacent one mi; ofthe strip, and an a utmentmember having a knife edge arranged to engage the strip midway between its two edges and-to extend longitudinally thereof. 5. A sound pick-up 4device comprisin a torsion strip, a mirror secured thereto, a 'a phragm, means connectin the diaphragm with the strip at a point ad] acent one edge of the stri an abutment member having a pair of knifg edges extending longitudinally of the strip arranged to'engage the strip at opposite sides ofthe connecting means, and means for adjustably supportingthe abutment member. f

In witness whereof, I have hereunto set my hand this 27th da of February, 1930.

LEW S T. ROBINSON. 

